The present invention relates to crystalline magnesium aluminum hydroxycarbonate of the formula EQU Al.sub.2 Mg.sub.6 (OH).sub.12 (CO.sub.3).sub.3.xH.sub.2 O or EQU Al.sub.2 O.sub.3.6MgO.3CO.sub.2.(x+6)H.sub.2 O,
respectively,
in which x is at least 4,
as well as to a process for manufacturing the product and antacids containing it.
Basic magnesium aluminum carbonates are known. For example, British Pat. No. 1,086,779 discloses carbonates of the formula EQU Al.sub.2 O.sub.3.xMgO.yCO.sub.2.zH.sub.2 O,
where x can be 0.15 to 1.5, y varies from 0.3 to 2.5 and z is no less than 2.5. These compounds are produced by conversion of magnesium carbonate, magnesium bicarbonate or a mixture of the two carbonates with an aqueous aluminum salt solution. British Pat. No. 1,086,779 states that it is of importance that the magnesium ions are present in quantities which are above the stoichiometrically required quantity in order to obtain products which contain magnesium. For 1 equivalent aluminum ions, 1.05 to 1.5 or more equivalents of magnesium ions are used. After precipitation, the basic carbonates are filtered out, washed and dried. They contain no more than 0.05 Mol % sodium and are suitable for use as antacid.
As a result of contacting the magnesium carbonate or bicarbonate with the aluminum salt, the magnesium aluminum hydroxy carbonates are obtained as a precipitate in the reaction mass. The mass may be filtered, washed, and dried in accordance with known techniques to obtain the final product, or it may be filtered, washed, and repulped to an aqueous slurry, or paste, to be incorporated in liquid antacids.
British Pat. No. 1,185,920 and corresponding DE-AS 1,592,126 disclose a process for preparing hydrotalcite which is known as a mineral having a chemical structure of the formula EQU Mg.sub.6 Al.sub.2 (OH).sub.16 CO.sub.3.4H.sub.2 O or Al.sub.2 O.sub.3.6MgO.CO.sub.2.12H.sub.2 O.
The process comprises forming a mixture, of pH at least 8, of an aluminum component selected from aluminum hydroxide, basic aluminum carbonate aluminum hydroxide - alkalimetal carbonate complexes, aluminum amino acid salts, aluminum alcoholate, water-soluble aluminates, aluminum nitrate, and aluminum sulphate, with a magnesium component selected from magnesium oxide, magnesium hydroxide, neutral and basic magnesium carbonates and water-soluble magnesium salts, in an aqueous medium in the presence of carbonate ion in a ratio in terms of Al.sub.2 O.sub.3 :MgO of substantially 1:6, and recovering the precipitated product.
British Pat. No. 1,598,375 and corresponding DE-OS 29 05 256 discloses a crystalline basic aluminum magnesium carbonate of the formula Al.sub.2 Mg.sub.6 (OH).sub.14 (CO.sub.3).sub.2.4H.sub.2 O.
The compound is prepared by a process which comprises heating a mixture of aluminum hydroxide and magnesium hydroxide in the appropriate molecular proportions in the presence of carbon dioxide in an aqueous medium containing ammonia or a water-soluble organic nitrogen-containing base at a temperature between 70.degree. and 100.degree. C. at atmospheric pressure, and separating from the reaction mixture the aluminum magnesium carbonate. The amount of ammonia or water-soluble organic base used is critical and quantities greater than 6 moles per mole of Al.sub.2 O.sub.3 present in the reaction mixture are necessary to ensure complete reaction. On completion of the reaction, the product is collected by filtration, washed with water and dried to give the product. British Pat. No. 1,598,375 and corresponding DE-OS 29 05 256 provide X-ray diffraction spectra of the compound produced according to these patents, and of hydrotalcite, both synthetic and natural.